1. Technical Field
This invention relates to a computerized numerical control unit for numerically controlling a machine tool or the like, and more particularly to a numerical control unit file protection system capable of protecting a file stored in a memory against an erroneous updating operation.
2. Description of the Related Art
Numerical control units (hereafter referred to as "NC units") are used in applying NC techniques to a variety of machines, and the filed of application thereof is ever widening. These NC units are now typically computers and are capable of implementing various functions by means of software. Recent NC units have a parameter control function in addition to the basic control software and are adapted to be able to store several files, with file names affixed thereto, in a submemory. By way of example, diagnosis and production management are facilitated if such information as the change in status of a machine with time, as well as the operating time, is filed. Files of this kind are capable of being modified by deletions, substitutions and changes in file name, even though the files contain information which is desired to be left unchanged.
The operation of NC units has become ever more simplified by adopting operator guidance displays and the like, and even an individual who does not possess a full understanding of NC units is capable of readily altering a file. Consequently, there are instances where important files that are not to be altered are deleted by an erroneous operation, such as by entering a file name incorrectly. A solution to this problem is desired.